Meltdown

Climate change is happening all around us, and one of the telltale signs is melting glaciers. We hear about it almost daily, pieces of ice the size of continents breaking off of Antarctica or the polar arctic ice breaking up and disappearing more and more quickly opening up navigational routes once unavailable due to thick winter ice cover. Will melting ice and glaciers so far away change our lives? Meltdown takes us deep into the cryosphere, the Earth’s frozen environment and picks apart why glacier melt caused by climate change will alter (and already is altering) the way we live around the world. From rising seas that will destroy property and flood millions of acres of coastal lands, displacing hundreds of millions of people, to rising global temperatures due to reflectivity changes of the Earth because of decreased white glacier surface area, to colossal water supply changes from glacier runoff reduction, to deadly glacier tsunamis caused by the structural weakening of ice on high mountaintops that will take out entire communities living in glacier runoff basins, to escaping methane gas from thawing frozen permafrost grounds, and changing ocean temperatures that affect jet streams and ocean water currents around the planet, glacier melt is altering our global ecosystems in ways that will drastically change our everyday lives. Meltdown takes us into the little-known periglacial environment, a world of invisible subterranean glaciers in our coldest mountain ranges that will survive the initial impacts of climate change but that are also ultimately at risk due to a warming climate. By examining the dynamics of melting glaciers, Meltdown helps us grasp the impacts of a massive geological era shift occurring right before our eyes.

Ocean Currents, Jet Streams, and Polar Bears

This chapter is divided into four sections, describing various impacts of glacier melt on different Earth ecosystems, including the effects of melting ice and water temperature on changes to ocean currents, on the global air Jet Stream, and on land surfaces, such as the popping up effect (the surface rebound effect) of the Earth once glaciers recede. It discusses the role of glacier meltwater for energy generation, as well as the impacts of the acceleration of glacier melt on flora and fauna, such as polar bears, salmon, and river bed and riparian biota.

Study of the jet stream over India and to its north in winter: Part I

Characteristics of the jet streams over India and to its north in winter were studied with the daily vertical cross sections (1200 GMT) along 75°E from 8oN to 60°N for the period I to 15 February 1967, It was observed that there are three separate jet cores present in this latitl1de belt on most of the days, located on an average at 43°N, 31°N and 23°N. of these three, the most stable and persistent one is the second which is located between Delhi and Srinagar, at 200-mb level with an average maximum speed of 140-150 kt. The one to its south is weaker and quite variable in location as well as altitude. The jet at 31°N, therefore, has been called the primary sl1b-tropical jet over India and its characteristics studied. Based on this study, a. model cross-section has been. prepared for this STJ, The descriptions of the STJ at 23°N and also of PFJ (Polar Front Jet) at 43°N are included.

Turbulence: Vertical Shear of the Horizontal Wind, Jet Streams, Symmetry Breaking, Scale Invariance and Gibbs Free Energy

The increase of the vertical scaling exponent of the horizontal wind Hv(s) with altitude from the surface of the Pacific Ocean to 13 km altitude, as observed by GPS dropsondes, is investigated. An explanation is offered in terms of the decrease of gravitational force and decrease of quenching efficiency of excited photofragments from ozone photodissociation with increasing altitude (decreasing pressure). Turbulent scaling is examined in both the vertical from dropsondes and horizontal from aircraft observations; the scaling exponents H for both wind speed and temperature in both coordinates are positively correlated with traditional measures of jet stream strength. Interpretation of the results indicates that persistence of molecular velocity after collision induces symmetry breaking emergence of hydrodynamic flow via the mechanism first modelled by Alder and Wainwright, enabled by the Gibbs free energy carried by the highest speed molecules. It is suggested that the combined effects have the potential to address the cold bias in numerical models of the global atmosphere.

Integration-based Extraction and Visualization of Jet Stream Cores

Jet streams are fast three-dimensional coherent air flows that interact with other atmospheric structures such as warm conveyor belts (WCBs) and the tropopause. Individually, these structures have a significant impact on the mid-latitude weather evolution, and the impact of their interaction is still subject of research in the atmospheric sciences. A first step towards a deeper understanding of the meteorological processes is to extract the geometry of jet streams, for which we develop an integration-based feature extraction algorithm. Thus, rather than characterizing jet coreline purely as extremal line structure of wind magnitude, our coreline definition includes a regularization to favor jet corelines that align with the wind vector field. Based on the line geometry, proximity-based filtering can automatically detect potential interactions between WCBs and jets, and results of an automatic detection of split and merge events of jets can be visualized in relation to the tropopause. Taking ERA5 reanalysis data as input, we first extract jet stream corelines using an integration-based predictor-corrector approach that admits momentarily weak air streams. Using WCB trajectories and the tropopause geometry as context, we visualize individual cases, showing how WCBs influence the acceleration and displacement of jet streams, and how the tropopause behaves near split and merge locations of jets. Multiple geographical projections, slicing, as well as direct and indirect volume rendering further support the interactive analysis. Using our tool, we obtained a new perspective onto the three-dimensional jet movement, which can stimulate follow-up research.

Cyclonic and anticyclonic contributions to atmospheric energetics

Migratory cyclones and anticyclones account for most of the day-to-day weather variability in the extratropics. These transient eddies act to maintain the midlatitude jet streams by systematically transporting westerly momentum and heat. Yet, little is known about the separate contributions of cyclones and anticyclones to their interaction with the westerlies. Here, using a novel methodology for identifying cyclonic and anticyclonic vortices based on curvature, we quantify their separate contributions to atmospheric energetics and their feedback on the westerly jet streams as represented in Eulerian statistics. We show that climatological westerly acceleration by cyclonic vortices acts to dominantly reinforce the wintertime eddy-driven near-surface westerlies and associated cyclonic shear. Though less baroclinic and energetic, anticyclones still play an important role in transporting westerly momentum toward midlatitudes from the upper-tropospheric thermally driven jet core and carrying eddy energy downstream. These new findings have uncovered essential characteristics of atmospheric energetics, storm track dynamics and eddy-mean flow interaction.

A Climatology of Atmospheric Rivers in New Zealand

The occurrence of extreme precipitation events in New Zealand regularly results in devastating impacts to the local society and environment. An automated atmospheric river (AR) detection technique (ARDT) is applied to construct a climatology (1979–2019) of extreme midlatitude moisture fluxes conducive to extreme precipitation. A distinct seasonality exists in AR occurrence aligning with seasonal variations in the midlatitude jet streams. The formation of the Southern Hemisphere winter split jet enables AR occurrence to persist through all seasons in northern regions of New Zealand, while southern regions of the country exhibit a substantial (50%) reduction in AR occurrence as the polar jet shifts southward during the cold season. ARs making landfall on the western coast of New Zealand (90% of all events) are characterized by a dominant northwesterly moisture flux associated with a distinct dipole pressure anomaly, with low pressure to the southwest and high pressure to the northeast of New Zealand. Precipitation totals during AR events increase with AR rank (five-point scale) throughout the country, with the most substantial increase on the windward side of the Southern Alps (South Island). The largest events (rank 5 ARs) produce 3-day precipitation totals exceeding 1000 mm. ARs account for up to 78% of total precipitation and up to 94% of extreme precipitation on the west coast of the South Island. Assessment of the multiscale atmospheric processes associated with AR events governing extreme precipitation in the Southern Alps of New Zealand should remain a priority given their hydrological significance and impact on people and infrastructure.

Are Cut-off Lows Simulated Better in CMIP6 Compared to CMIP5 ?

This is the first study to show the global Cut-off Low (COL) activity in 23 models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) and 17 models from Phase 6 (CMIP6). The COL historical simulations for the period 1979-2005 obtained from the CMIP5 and CMIP6 models and their ensembles are compared with the ERA5 reanalysis using an objective feature-tracking algorithm. The results show that the CMIP6 models simulate the spatial distribution of COLs more realistically than the CMIP5 models. Some improvements include reduced equatorward bias and underestimation over regions of high COL density. Reduced biases in CMIP6 are mainly attributed to the improved representation of the zonal wind due to the poleward shift of the subtropical jet streams. The CMIP5 models systematically underestimate the COL intensity as measured by the T42 vorticity at 250 hPa. In CMIP6, the intensity is still underestimated in summer, but overestimated in winter in part due to increased westerlies. The overestimation is enhanced by the finer spatial resolution models that identify more of the strong systems compared to coarser resolution models. Other aspects of COLs such as their temporal and lifetime distributions are modestly improved in CMIP6 compared to CMIP5. Finally, the predictive skill of climate models is evaluated using five variables and the Taylor diagram. We find that 10 out of the 15 best CMIP5-CMIP6 models belong to CMIP6, and this highlights the overall improvement compared to its predecessor CMIP5. Despite this, the use of the multi-model ensemble average seems to be better in simulating COLs than individual models.

Evaluation of flight conditions at tropopause level

High-quality organization of meteorological support along the flight routes, increasing its efficiency depends on many factors. These factors include the moderate and high intensity turbulence observed in the middle and upper flight echelons, icing, jet streams, volcanic ash clouds and their distribution areas, tropopause level, its altitude, and others. In the pre-flight preparation phase, the meteorological body provides meteorological support for all types of domestic and international flights planned in the middle and upper troposphere. The organization of flight efficiency and economic profitability depends on the high-quality forecast of the above-mentioned meteorological factors. The article analyzes the characteristics of weather conditions that affect flights in the middle and upper troposphere. The main recommendations and requirements of Annex 3 (ANEX 3) and its amendments (Amendment 79), ICAO's guidelines for meteorological support for international air navigation, are relevant to many of the issues discussed in this article. Key words: turbulence, jet stream, volcanic ash, aircraft, tropopause, aviation, flight echelon, pressure, wind, temperature, meteorological support, flight route